(a) Field of the Invention
The present invention relates to spreader frames as used in cargo handling equipment such as straddle carriers. Spreader frames are a form of grappling device for making connection with elongated loads typified by standardized, rectangular shaped shipping containers and trailer truck vans. They connect onto such loads at substantially spaced points along their lengths and are used for lifting and supporting the load during short hauls from one site to another.
(b) Description of the Art
Vehicles for lifting and transporting large, box-shaped shipping containers and transporting them for short distances have become specialized. Straddle carriers are one form of this type of equipment, and in general they are characterized by having a central bay defined by two spaced sides and an arch-like structure connecting the sides that bridges over the bay. A straddle carrier is adapted to be driven over a load, such as a container or van, to receive the load within the bay, and there is provided an elongated spreader frame suspended from the arch-like construction that connects onto the load. By raising the spreader frame the load is elevated for transport, or for stacking one container upon another by utilizing the frame as an elevator. In some straddle carriers the bay is sufficiently large so that by turning the spreader frame the load can be shifted in its orientation, and it is consequently desirable to suspend spreader frames in such fashion that they can turn or reorient the load without moving the entire straddle carrier.
Spreader frames are typically adjustable in length to match that of the loads they are to pick up. The loads can then be lifted at their ends, and it is common in the field of containerization to provide receptor portions of standardized twist-lock type connecting members at the upper corners of the loads for engagement with spreader frames. Shipping containers and trailer vans are usually of standard lengths, such as twenty or forty feet, and spreader frames are set to similar lengths to connect with the loads they are to pick up. In working with such long lengths, there is the problem of aligning a spreader frame with the intended load in order to make connection. The connection can either be in the form of twist-locks at the four upper corners of the load, as mentioned, or a spreader frame may be equipped with depending legs with shoes at their lower ends that encircle underneath the load for lifting it along its bottom. Whichever form of connection is made, the spreader frame must be accurately positioned so that a proper connection is made, and so that the container or van will not be damaged. Often the sides of these loads are quite fragile, and the structurally strong points are at the corners where connection is to be made.
It is unsatisfactory to maneuver the entire straddle carrier in order to align the spreader frame with the load, and the art has addressed itself to this problem by providing some controlled degree of longitudinal and lateral movement of the spreader frame with respect to the straddle carrier chassis. For example, in U.S. Pat. No. 3,982,644 a spreader frame is supported by four hoist cables connected to its four corners, and one end of the frame can be shifted either sidewardly, or turned so as to skew the entire frame. This gives some capability for aligning the spreader frame with respect to a load, and in this particular patent hydraulic cylinders are employed that are connected between the spreader frame and vehicle chassis for shifting the frame with respect to the chassis. However, this only provides a limited degree of adjustment of the spreader frame in a horizontal plane, and does not provide any capability of making a substantial movement of the spreader frame or a significant reorienting of the load once it is lifted.
U.S. Pat. No. 3,520,431 discloses a spreader frame with sensing blades hanging downwardly from its sides. When the frame is brought over a load and then lowered for making connection the sensing blades detect misalignment of the frame with the load. Through an electrical circuit a pair of hydraulic cylinders are operated to rotate the frame or shift it sidewardly to obtain alignment in a transverse direction. However, the entire straddle carrier has to be moved to obtain alignment in the longitudinal direction. Also, the shiftable frame has to be suspended from a second vertically movable frame which requires additional structure. Again, as in the preceding patent, there is only a limited amount of available movement of the frame, and it is impractical to make substantial shifts in the position of a load once it is raised.
The art has not provided a suspension for a spreader frame that will give greater mobility for the manipulation of loads, or for swinging the spreader frame through substantial arcs to give greater versatility to straddle carriers with which they may be used.